Generally, semiconductor devices are used in a variety of electronic applications, such as computers, cellular phones, personal computing devices, and many other applications. Home, industrial, and automotive devices that in the past comprised only mechanical components now have electronic parts that require semiconductor devices, for example.
Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece or wafer, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semiconductive, and insulating materials that are patterned and etched to form integrated circuits (ICs). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip, for example.
Optical photolithography involves projecting or transmitting light through a pattern comprising of optically opaque areas and optically clear or transparent areas on a mask or reticle. For many years in the semiconductor industry, optical lithography techniques such as contact printing, proximity printing, and projection printing have been used to pattern material layers of integrated circuits. Lens projection systems and transmission lithography masks are used for patterning, wherein light is passed through the lithography mask to impinge upon a photosensitive material layer disposed on a semiconductor wafer or workpiece. After development, the photosensitive material layer is then used as a mask to pattern an underlying material layer. The patterned material layers comprise electronic components of the semiconductor device.
There is a trend in the semiconductor industry towards scaling down the size of integrated circuits, to meet the demands of increased performance and smaller device size. However, as features of semiconductor devices become smaller, it becomes more difficult to pattern the various material layers because of diffraction and other effects that occur during a lithography process. For example, key metrics such as resolution and depth of focus of the imaging systems may suffer when patterning features at small dimensions.
Lithographic enhancement techniques have been aggressively pursued and adopted to overcome these limitations. These techniques relate to improvements in the optical systems (exposure apparatus), types of masks (phase shift masks, trimming masks, etc.), or the resists. Recently, attenuated phase shifting has been pursued as one means to enhance lithography. However, such enhancements to lithographic techniques may also increase manufacturing costs.
What are needed in the art are lithography masks and methods of manufacture thereof that are cost-effective while still retaining the benefits of lithography enhancing techniques such as attenuated phase shift mask.